This invention relates to dipole antenna systems and more particularly to a circularly polarized dipole antenna system for FM and TV broadcast. The term circularly polarized as used herein refers to the general class of elliptically polarized antennas with low axial ratio.
Circularly polarized omnidirectional antennas using slanted or tilted dipoles are known. See, for example, an article in RCA Review dated June 1947, Vol. VIII, No. 2 entitled, "Circularly-Polarized Omnidirectional Antenna" by George H. Brown and Oakley M. Woodward, Jr., pp. 259 thru 269. Also, see Lindenblad U.S. Pat. No. 2,217,911. In these arrangements, four slanted dipoles are fed in-phase or in a mode zero (H=O) condition. Although the antenna system as described in this art operates adaquately when the antenna system is mounted at the top of a mast, this arrangement is not practical with support masts where antenna systems are to be stacked one upon the other, because of undesired re-radiation of the support masts. Also, undesired re-radiation occurs from the horizontal support members supporting the radiating dipoles. These re-radiations cause unwanted perturbations in the desired elevation patterns.
P. S. Carter in the Proceedings of the IRE, Dec. 1943, pp. 671 thru 693, entitled, "Antenna Arrays Around Cylinders" discusses arrays of dipoles around spires or other supports. Carter discusses four horizontal or vertical dipoles fed in-phase rotation about the cylinder to achieve an omnidirectional pattern for a horizontally polarized or vertically polarized signal. No solution or discussion is presented with regard to obtaining omnidirectional circularly-polarized radiation.
An article by the present inventor in Mar. 1965 issue of RCA Review entitled, "A Mode Analysis of Quasiisotropic Antennas," pages 42 through 74, discusses obtaining an antenna pattern having rotational symmetry with respect to a reference axis which consists of the superposition of one or more independent decoupled mode types, each of which has a symmetrical radiation pattern. For any given mode, the orientation of the radiators is either axial, tangential, or radial.